The present invention relates to a memory circuit, and more particularly to a memory having a redundant structure. The memory capacity of semiconductor memories has been increased to the point where memories having a 256k-bit capacity have become commercially available. However, the increase in the memory capacity has resulted in low fabrication yields due to the low probability of all circuit elements on such a dense structure being fabricated without defect. Hence, it has become difficult to obtain a memory in which all the constituent elements are good.
To reduce the above problem, memories having redundant structures have been developed and are widely utilized. In a memory having a redundant structure, a redundant array of memory cells is provided in addition to a normal array of memory cells. If a cell or cells in the normal array are faulty or defective, such defective cells are replaced by good cells in the redundant array, so that a functionally good memory can be obtained even though defects may be present in the normal array. Information as to the address of the replaced cells is stored by a program circuit which includes a plurality of programmable read only memory cells. When the defective cell in the normal array is addressed from the outside, the program circuit operates to inhibit accessing of the defective cell and to cause accessing of replacement cell or cells in the redundant array. Therefore, as viewed from outside the memory, it appears as if all cells in a normal array are accessable and free of defects.
Each of the programmable read only memory cells in the program circuit is formed of a fusible link and at least one transistor serially connected between power supply terminals. The cells are programmed by selectively cutting the fusible link by a trimming technique. As a result, some of the fusible links are cut while others remain uncut, according to the desired programmed state. However, according to this prior art technique, a DC current inevitably flows through the read only program cell when the fusible link remains uncut. Accordingly, relatively large power consumption results.